In this activity, students collect and analyze data adapted from recent research that explores the correlation between the presence of fish farms and mortality rates in wild salmon runs adjacent to the fish farms. Students then relate their findings to nearby populations of orcas to theorize how a decline in the wild salmon population could affect orca populations.

VOCABULARYanadromous fish — fish that migrate from freshwater to saltwater aquaculture ("aqua" = water, "culture" = till or cultivate) — the raising or farming of saltwater or freshwater organisms, like fish or oystersclosed-containment technology — the use of closed tanks in aquaculture to keep effluence and chemical additives from entering the surrounding waterectoparasite ("ecto" = outer) — an organism living on the outside of another organism, the host; parasites get their energy from their host, causing harm or even death to the host infestation — the presence of pests or parasitesload — the number of parasites on a host organismopen-net cage — a containment, commonly used in fish farming, in which water flows freely through the nets, allowing food, waste and other additives to pass into the surrounding environmentsea louse (pl.: lice) — a type of crustacean that parasitizes marine organisms; one species of sea lice, Lepeophtheirus salmonis, lives exclusively off the skin, blood and mucus of salmonspawn — releasing eggs and sperm into the water

BACKGROUND

The wild salmon of the Pacific Northwest
The five species of salmon native to the Pacific coast of North America (Chinook, pink, coho, sockeye and chum) are keystone species in each of the interdependent freshwater, land and coastal marine systems that define the Pacific Northwest. From highland coniferous forests to rocky coasts, temperate rain forests to freshwater streams, salmon are an important thread in the natural fabric of the region. Salmon are anadromous fish, meaning they migrate from freshwater nurseries to the ocean and back again to spawn. On their extraordinary journey from cool riverbeds snaking through shady forests to the open waters of the Pacific Ocean, salmon provide food for animals at each level of the energy pyramid. The food web even links salmon species to one another. Pink and chum salmon are very small when they begin to migrate out to sea. When they are young, these two species of salmon are eaten by larger species, such as Chinook salmon, creating a vital link among the members of the salmon group.

How are wild salmon and orcas connected?
All five species of salmon feed the two endangered Pacific coast resident orca communities. These orcas are fish feeders, deriving upwards of 90 percent of their diet from salmon. The northern resident orcas, numbering around 200 individuals, and the southern resident community, of 83 orcas, rely directly on the wild salmon stock for their survival. Studies have estimated the southern resident community alone consumes 500,000 20-pound fish a year! As wild salmon populations decline, resident orcas have been sited as far south as Monterey and Los Angeles, well beyond their traditional ranges.

Sea lice and salmon
A sea louse is a tiny ectoparasite, an organism that lives on the outside of another organism, potentially causing harm, even death. These tiny organisms have evolved with their host, the salmon, and developed specialized legs for holding on while feeding on their skin. Sea lice are native to Pacific waters and do not present a problem for adult salmon, but they are a grave problem for juvenile salmon. On a young fish, a single louse can create lesions on the skin that can cause secondary infections or a loss of blood resulting in death.

Sea lice are not the only threat facing salmon. Water diverted for agriculture and human consumption alter the flow of the rivers and streams used by salmon to spawn and support their fry. Salmon also suffer the effects of elevated levels of chemical pollutants. These toxins remain in their tissue and accumulate. None of this is good news for orcas, as their fate is intimately linked to the fate of wild salmon.

Fish farms in the Pacific Northwest
When you think of the Pacific Northwest, you think of salmon. Salmon are undeniably important to the area's economic health, and they are an important part of the cultural heritage of the region. Salmon fuel the economy by providing an influx of people, money and food into the area. In recent years, as wild salmon runs have declined, aquaculture, the farming of fish in near-shore holding tanks, has grown as an industry. In most locations, farmed fish grow up in what are called open-net cages. These containers allow water to flow through the farmed stock and mix with the surrounding ocean water. Fish farms are located in protected coves and in other near-shore locations where access is easiest. Fish farms are found worldwide. The industry is thriving along the Pacific Northwest coast, with more than 100 fish farms in British Columbia alone.

Proponents of fish farming defend the practice as reducing fishing pressure on wild salmon stock while creating jobs and food for a growing human population. Detractors cite the environmental impacts of raising large quantities of fish in a limited space. Effluence composed of fish waste, food scraps, antibiotics and other drugs used to combat parasites and disease flows into the surrounding water. These by-products elevate nitrogen levels and lead to damaging changes in bottom fauna and water quality in critical habitat for juvenile fish and marine invertebrates. Advocates for salmon, the orca and other iconic Northwest coast species see closed-containment technologies as a viable solution for these drawbacks to the industry.

Cut up the mortality cards and place them in an envelope for distribution during round 4.

Post the sea lice sign on one side of the room.

PROCEDURENote: Parasite Perils is based on data gathered by Alexandra Morton, Richard Routledge, Corey Peet and Aleria Ladwig in the Broughton Archipelago. The relationships between the numbers in the game accurately reflect the sea lice infestation levels recorded in the study, though the sample size has been changed to accommodate a classroom setting and to simplify the computations.

The game is based on a sample size of 25,000 and a class size of 25 students. Adjust the game to larger class sizes by partnering students or adjust to smaller class sizes by giving some students additional cards. To arrive at the correct ratios, all 25 cards MUST be used. Additional students can also record data on the board and pick the numbers from the bowl.

Tell the students that they will be exploring the research question "Do salmon farms affect wild salmon populations through the spread of sea lice to juvenile salmon?" In this activity, they will collect and analyze data to answer the question.

Pass out the salmon sheets and student worksheets to each student. Be sure to use all 25 salmon cards. Explain that each card represents 1,000 juvenile pink salmon, with a total sample size of 25,000.

Pass out one set of the number cards or have the students count off 1 through 25 so that each student has a number and all 25 numbers have been assigned.

Optional: Designate one area in the room for salmon free of lice (surviving side) and one for sea lice-infested salmon (mortality side). All of the infested salmon die. Have students stand up and move from one side to the other as the game unfolds to increase involvement.

Explain that the game has four rounds and that each round addresses a different part of the research on wild salmon and sea lice.

Read the script accompanying each research question and direct students to record the data on their worksheets.

After each round, return all number cards to the envelope and ask all students to return to the "alive" side of the room.

Once all the data have been collected, ask students to use the numbers to compare the sea lice infestation levels at the three sites: away from fish farms, near fish farms and next to fish farms.

Tell students to create two histograms, one showing the actual number of salmon with sea lice at each of the three locations and another illustrating the percentage of infested salmon in the sample at each site.

Have students use their graphs to answer the questions on their worksheet.

Have students share their histograms and answers in a brief class discussion.

Briefly share and discuss the other issues and solutions related to fish farming that are outlined in the background section.

End the class with a discussion on how a decline in the wild salmon population affects ecosystems, the populations of orcas that depend on the salmon for food and us. Does it matter if the wild stocks of salmon crash if we now have farmed salmon to eat? Why? What does this mean for the marine and terrestrial ecosystems of the Pacific Northwest? What are possible solutions? What other studies are needed?

EXTENSIONS

Have students debate the pros and cons of fish farming.

Salmon face other threats, such as dams and chemical pollutants. Have students research these threats and share how these elements put additional pressures on salmon and orca populations.

ADDITIONAL RESOURCES
Aquaculture: Down on the Farm
A lesson that introduces students to the complex social, economic, environmental and technological aspects of aquaculture from the public television series QUEST: Investigating Our Worldhttp://www.mpbn.net/quest/pdf/aquaculture_ml.pdf (PDF)

Essential Principle #6: The ocean and humans are inextricably interconnected.

ABOUT THE AUTHOR
Amy O'Donnell is a science curriculum specialist for Columbia University's Center for Environment, Economy and Society and is an independent contractor for KQED Education Network. KQED Education Network uses the power of KQED Public Broadcasting to inspire learning by providing projects for youth and curriculum materials and professional development for teachers, child-care providers and families.

CREDITSJean-Michel Cousteau: Ocean Adventures is produced by KQED Public Broadcasting and the Ocean Futures Society. The corporate sponsor is the Dow Chemical Company. Additional major support comes from the Richard and Rhoda Goldman Foundation, KQED Campaign for the Future, and the Corporation for Public Broadcasting.